<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <script>
        // 页面加载事件: 当整个网页加载完成后触发页面加载成功事件,调用对应的函数执行
        onload = function () {
            //1.获取事件源对象
            let btnObj = document.getElementById("btnId");
            //2.派发事件
            btnObj.onclick =  function () {
                alert("4494444444444");
            }
        }

    </script>

</head>
<body>
    <input type="button" value="再点我44" id="btnId"/> <br>
</body>
</html>
